I tried the Unhappy Girl deck on Lvl 40. I've got Unhappy girl on the field and tried to block is Stone Soldier. He used OtC and I tried to negate it with Riryoku Field but it didn't work?!
Are you attacking in the same turn you set your Riryoku Field? And the OTC already set on his field? If that the case, then yes, you can't use Riryoku Field the turn you set it.